The present invention relates to a dye-containing mass, composition containing it and method for dyeing keratin fibers, especially human hair.
The use of ground plants for dyeing of hair has in principle been known from antiquity. Customarily pulverized or ground plant parts from plants which are most effective for dyeing purposes, such as Indigo leaves or Henna are used, are stirred with water, filler materials and thickeners to form a dye paste and then this dye paste is applied to the hair. This process has however the disadvantage that the dye powder must be ground very fine in order to dye the hair uniformly. Furthermore in many cases the dye does not penetrate into the hair and water-insoluble components remain on the hair which are only washed out of the hair completely with great difficulty. Finely grinding up the dye has the disadvantage that the preparation and processing of it is accompanied by the production of an unpleasant dust. Extraction of natural materials from the appropriate plants and processing the extract to obtain a dye preparation has already been attempted. The dye substances isolated from the plants by extraction are however very unstable to the effects of oxygen and light and are unsuitable for making stable dye compositions.
The Indigofera plants contain Indicane(the dye precursor of Indigo) which can be easily cleaved by hydrolysis into indoxyl and glucose. The indoxyl obtained thereby is converted into Indigo already by action of oxygen. Indigo is a blue dye with good fastness properties and has been used to dye textile materials for a thousand years. Since Indigo is water insoluble however this dye must be converted into a water soluble form(the so-called indigo bath solution) by a reduction process, for example by means of an alkaline hydrogen sulfite solution. A process of this type is however of little practical value for dyeing hair.